In a typical vehicle air-conditioning system, refrigerant is compressed by a compressor unit driven by the automobile engine. The compressed refrigerant, at high temperature and pressure, enters a condenser where heat is removed from the compressed refrigerant. The refrigerant then travels through a receiver/dryer to an expansion valve. The expansion valve throttles the refrigerant as it flows through a valve orifice, which causes the refrigerant to change phase from liquid to a saturated liquid/vapor mixtures as it enters the evaporator. In the evaporator, heat is drawn from the environment to replace the latent heat of vaporization of the refrigerant, thus cooling the environmental air. The low-pressure refrigerant flow from the evaporator returns to the suction side of the compressor to begin the cycle anew.
The high pressure refrigerant flow through the expansion valve must be regulated in response to the degree of superheat of the refrigerant flow between the evaporator and suction side of the compressor to maximize the performance of the air-conditioning system. The superheat is defined as the temperature difference between the actual temperature of the low-pressure refrigerant flow and the temperature of evaporation of the flow.
Thermostatic expansion valves typically include a power element comprising a diaphragm mounted between a domed head and a support cup on the valve body. A “charge” is located within a head chamber defined by the domed head and one (upper) surface of the diaphragm. The support cup and the other (lower) surface of the diaphragm define a diaphragm chamber with the body of the expansion valve. A valve stem extends downwardly from the diaphragm through a bore in the valve body to a valve element modulating a valve orifice between a first port in the valve body (to the condenser) and a second port in the valve body (to the evaporator).
To control the refrigerant flow, the diaphragm in the power element moves in response to the refrigerant condition exiting the evaporator and compensates the flow rate to the evaporator by opening or closing the valve orifice.
A trend in the industry is toward block-type (“bulbless”) thermostatic expansion valves. In such valves, the outlet flow from the evaporator is directed back through the block valve and is used to regulate the response of the diaphragm. In certain bulbless valves, a thermally conductive pressure pad is located against the lower surface of the diaphragm. As the refrigerant passes around the pressure pad, heat energy is transferred by conduction through the pad to the refrigerant charge in the head chamber above the diaphragm valve. A portion of the diaphragm surrounding the pressure pad is typically also exposed and in direct contact with the refrigerant. Refrigerant pressure from the evaporator outlet against the diaphragm along with the force of an adjustment spring on the valve element tends to close the valve, while pressure from the charge tends to open the valve. The balance of forces across the diaphragm along with the spring constant of the diaphragm determine the deflection of the diaphragm and hence the opening of the expansion valve orifice between the condenser and evaporator. The diaphragm deflects as appropriate to maintain a balance between these forces.
Glennon et al., U.S. Pat. No. 4,984,735; Fukuda, U.S. Pat. No. 6,223,994; Proctor, U.S. Pat. No. 3,691,783; Treder, U.S. Pat. No. 3,537,645; and Orth, U.S. Pat. No. 3,450,345, show and describe examples of block-type bulbless expansion valves such as described above.
There are numerous techniques known for attaching the refrigerant tubes from the various components to the block valve such that fluid can be directed into or out of the valve. One technique is to insert the tube into a bore in the block and secure the tube such as by soldering, welding, or brazing. This technique is shown in U.S. Pat. No. 4,095,742. Alternatively, a fitting can first be attached to the valve block with cooperating threads, such as shown in U.S. Pat. No. 3,450,345; or by soldering, welding or brazing, such as shown in U.S. Pat. No. 4,852,364, and the tube can then be attached to the fitting (such as by friction fit, cooperating threads, flared flange, etc.).
It is also known to form an annular bead toward the end of the tube, and locate the bead within a counterbore formed in the block valve. An O-ring type seal can be located between the bead and the shoulder to fluidly seal the tube in the bore. A retaining plate with appropriately-sized openings is received around the tube and is fastened such as by a bolt to the block valve. This technique is shown in U.S. Pat. No. 5,269,459.
While the above techniques can be useful in certain situations to attach a tube to a block valve, they are not without drawbacks. Providing a fitting for example, requires a separate component with its own material, machine steps, and stock-keeping costs. A retaining plate also requires additional material, machining steps and stock-keeping costs. Forming threads on the block valve is also a time-consuming step. Soldering, welding and brazing raise environmental concerns.
Thus, it is believed that there is a demand in the industry for an effective and efficient technique for attaching a fluid tube to a block valve which reduces material waste, machining steps, stock-keeping units, and which does not raise environmental concerns.